Embodiments in accordance with the present invention relate to a method of assigning logical block addresses and a data writing method of a disk drive, in particular, to an assigning method of logical block addresses, a disk drive, and a data writing method where a plurality of track widths exist.
One of the methods to improve the recording density of a disk drive is to reduce the track width and track density. A means for achieving these objects is to miniaturize the write and read heads of the disk drive. The miniaturization of these heads enables data to be written on a track of a narrower width, and the reduction of track width leads to improvements in track density. The write and read head is fixed on the arm, and its arm is driven by a voice coil motor. Because of the mechanical structure of driving the arm by the voice coil motor, the displacement of the arm is subject to errors resulting in the write head jutting out of the track into which writing is made into both sides of the track at the time of writing on the track and the destruction of data. In order to prevent such destruction of data, the interval between two tracks is kept larger than the track width to secure a write margin. An approximately 10-percent margin is secured for the write margin on both sides of a track hindering the improvement of track density. Any disk drive in which data are written arbitrarily in a sector requires write margins on both sides of each track. However, the adoption of a sequential writing mode enables one side of the write margins to be deleted, and therefore the track density can be improved to that extent. In other words, even if the same write head, read head, or storage medium is used, the capacity of the disk drive can be improved by approximately ten percent.
As the interval between two tracks cannot be made narrower than the width of the write head according to the ordinary writing method of the disk drive, the write head width determines the minimum track interval. Accordingly, in order to improve the capacity of a disk drive to an extent farther than the deletion of a write margin, a method of reducing the track width to narrower than the width of a write head is required. Such methods disclosed by the U.S. Pat. No. 6,185,063 and W099/45534 reduce the track width rather than the write head width by partially overwriting data on the adjacent tracks.
U.S. Pat. No. 6,185,063 proposes two methods called “write seldom format” and “paired format” as partially overwriting methods on tracks. The “write seldom format” improves the reduction ratio of track width by partially overwriting data alternatively on a plurality of tracks instead of disabling to overwrite data in a random order on any arbitrarily chosen track. On the other hand, the paired format causes the reduction ratio of track width fall instead of enabling overwriting data in a random order on an arbitrarily chosen track by partially overwriting data on two adjacent tracks.
Ordinary disk drives recognize only linear address spaces represented by the logical block address (LBA) and do not recognize the logical structure of data such as file and directory. As a result, the file system in the operating system (OS) of high-order devices manages the logical structure of data and the arrangement of data in the disk drive. On the other hand, in the disk drive supporting the object based device commands (OSD) described in the T10/1355-D information technology—SCSI OSD (refer to SCSI Object Based Device Commands (OSD), incorporated by reference herein for all purposes, the disk drive can understand the data structure by offloading a part of the functions of the file system on the disk drive side. In other words, according to OSD the data (objects) written in a disk are recognized not by LBA but by the object ID.